The 'halo effect' may be unique to different raters or common to all raters. When common to all raters, halo is not detectable through standard fit indices of the three-facet Rasch model used to account for differences in rater severities. Using a formulation of halo as a violation of local independence, a halo effect common to all raters is simulated and shown to be diagnosable through contrasts between two-facet stack and rack Rasch analyses. In the former, the thresholds are clustered and the distribution of persons is multimodal; in the latter, all thresholds are close together and the distribution of persons is unimodal. In the former, the scale is stretched, and the person separation inflated, relative to the latter.